In the manufacturing or factory setting, customer orders for various items need to be processed in a certain amount of time (i.e. by a shipment date). For each item ordered which is not already in inventory, the item must be manufactured. To manufacture the item, certain resources (materials, machine time, man hours, etc.) used in a predetermined sequence of events are required. In order to efficiently utilize the resources of the manufacturing plant in such manufacturing of items, and ultimately in fulfilling a multiplicity of orders, the manufacturer generally employs a device for scheduling the use of different resources at different dates and time.
Various scheduling methods exist to aid in and/or optimize such scheduling of resources. Typically, scheduling methods are based on one of two scheduling techniques, forward scheduling or backward scheduling. Briefly, in forward scheduling the sequence of desired manufacturing steps is scheduled beginning at the current date and from then into the future. The capacity of resources influences how far into the future steps are scheduled. Backward scheduling schedules the sequence of manufacturing steps in reverse order from the shipment date backward in time toward the current date without regard to the capacity of the resources required.
Other scheduling methods concern the planning of materials required in the manufacturing process. Scheduling devices which employ these scheduling methods are generally referred to as materials requirement planning (MRP) systems. Typically, MRP scheduling systems assume an infinite capacity of machinery, man hours, etc. and determines the amounts and types of materials that must be on hand at particular dates/times for a given manufacturing plant with given orders.
"Production Management Concept Cuts Delay, Budget Overruns" by J. C. Lowndes, Aviation Week and Space Technology, Volume 122, No. 19, Pages 85-87, May 13, 1985 discloses a scheduling software device called Opt (Optimized Production Technology). The Opt software combines capacity planning with forward scheduling and backward scheduling for "unconstrained" or infinite capacity resources. The core Opt module is a finite forward scheduler that uses resource capacity, orders and inventory data for optimum output from the resources. The core Opt module determines the hour and minute of each day at which bottlenecks or constrained processes will occur, and provides an indication of which due dates will be missed and by how much time the dates will be missed with the current plant configuration. A backward scheduling module of Opt assumes infinite capacity and schedules non-bottleneck processes beginning at the completion times determined by the core module. This ensures that material is available for the first operation in the critical part of the manufacturing process.